Providing adequate energy to power all the various needs of society is becoming more problematic every year. Conventional sources such as coal, petroleum and gas, are becoming more expensive and harder to find. At the same time, the byproducts of combustion produce air pollution and elevate atmospheric carbon dioxide, threatening severe consequences for the global environment.
A technology currently capable of providing high capacity energy storage is pumped hydro. An example of this technology is shown in the system 10 of FIG. 1. With reference to FIG. 1, the system employs two large water reservoirs 102 and 105 located at different elevations with respect to each other. Water 106 is pumped by pump 101 from the lower reservoir 102 to the higher reservoir 105 whenever excess energy is available, and the excess energy (minus any losses due to inefficiencies) is stored in the system 10. (The excess energy is generated by power grid 108 and powers electric motor 100 via substation 107.) Energy stored in the system 10 is released as follows. Water 106 is released from the higher reservoir 105 through hydraulic turbine 103 into the lower reservoir 102 to produce mechanical energy. The mechanical energy is converted into electric energy by generator 104 and provided to the power grid 108 via substation 107.
Large-scale installations of systems such as system 10 can provide a peak output power of more than 1000 megawatts (MW) and a storage capacity of thousands of megawatt-hours (MW-H). Pumped hydro has been a common bulk storage technology for decades, providing capacity worldwide. However, geographic, geologic and environmental constraints associated with the design of reservoirs for such systems, in addition to increased construction costs, have made this technology much less attractive for future expansion. Thus, this technology may not provide a practical method to provide the wide applicability, capacity, low cost and environmental compatibility required to support the needs of future expansion, which may include, for example, a conversion of the energy infrastructure from hydrocarbon sources to renewable sources of energy.